This invention relates generally to axial-thrust bearings and more particularly to high performance thrust roller bearings which provide enhanced removal of frictional heat and replenishment of a lubricant film by assuring lubricant flow through the bearings to other components of a rotating machine.
In automotive transmission units as well as in other high-speed rotary machines, lubricant circulation is the primary mechanism for dissipation of frictional heat. The rollers are aligned on the radii of the bearing, and the sidewalls of the pockets are offset but parallel to the radii. The rollers, being narrower than the pockets are slightly loose within the pockets, and while driving the cage during acceleration and being driven by the cage during deceleration, the rollers tend to contact the sidewalls at the outer end rather than along the full length of the roller. This results in almost point contact between the outer end of the rollers and rectangular roller pockets of the roller cage at the outer ends of the roller pockets and leads to increased local heat generation and wear of the cage and rollers. Apart from that, the sliding local contact between the rollers, the cage, and the races produces frictional heat and, in cases of inadequate lubricant flow, can generate temperatures sufficient to degrade seals, lubricants, and friction linings. This may result in constriction of fluid paths due to accretion of wear particles and lubricant breakdown products, accelerated wear of moving components due to further decrease of already inadequate lubricant flow, and increased rates of frictional heat generation. Since much of the lubrication of components mounted radially outboard of the thrust bearing relies on lubricant which must pass through the bearing, any factor which impedes such flow or degrades its effectiveness is potentially catastrophic to the life of the transmission. Moreover, there is a tendency for lubricant to follow the path of least resistance through the bearing, thereby contributing to lubricant starvation of other critical areas of the bearing. Thus, lubricant, in order to provide the maximum protection, must be directed away from paths of least resistance and into those parts of the bearing which carry the greatest load and which generate the greatest frictional heat effects. For applications requiring higher power density, higher rotational speeds, and increased roller loading, it is important to minimize or to completely avoid the above lubrication inadequacies.
The foregoing illustrates limitations known to exist in present high performance roller thrust bearings for use in rotating machines. Thus, it would be advantageous to provide an alternative directed to overcoming one or more of the limitations set forth above. Accordingly, a suitable alternative is provided including features more fully disclosed hereinafter.